1. Field of Invention
The present invention relates generally to microgrids for controlling industrial scale distributed energy resources (DERs). More specifically, the present invention relates to a system and method for controlling different operating states of a microgrid with DC and AC inputs and outputs.
2. Description of Related Art
In general, microgrids are electric networks that are capable of deriving power from a number of sources including the conventional power grid, localized power generating capabilities using renewable generating resources, and alternative power sources such as solar arrays and wind turbines. The microgrid can aggregate power from a number of sources, converting the different formats of power derived from multiple and diverse sources to common voltage and frequency formats that can be subsequently distributed to one or a number of loads. In addition, the microgrid can maintain the reliability of power to one or a number of loads in the face of changing power levels that are derived from the multiple and diverse sources. A microgrid can be coordinated to provide power from a variety of power sources and to provide power with greater reliability. For example, a microgrid can provide an alternate source of power to a site when there is an interruption in the power delivered by the conventional utility power grid. A microgrid also can provide an alternate source of power, such as power from a renewable energy source, when renewable energy is preferred over power delivered by the conventional utility power grid. The power that the microgrid supplies to a site may be derived from a variety of sources including energy storage devices, alternative energy sources such wind or solar power, or from burning conventional fossil fuels. A description of prior art microgrid configurations is found in the whitepaper entitled “Characterization of Microgrids in the United States” prepared for Sandia National Laboratories by Resource Dynamics Corporation dated January 2005 and incorporated herein by reference in its entirety.
In general, there are prior patents and published patent applications directed to various aspects of microgrids. For example, U.S. Pat. No. 6,819,087 discloses a distributed resource stabilization control for microgrid applications. U.S. Pat. No. 6,778,414 relates to a distributed system and methodology for electrical power regulation, conditioning and distribution on an aircraft. U.S. Pat. No. 6,765,370 discloses a system and method for bi-directional power conversion in a portable device. U.S. Published Patent Application No. 2008/0143304 describes a system and method for controlling a microgrid.
The disclosures in these prior patents and published patent applications is hereby incorporated herein by reference in their entirety. However, as described further below, none of these prior patents or published patent applications provides the solutions of the invention described and claimed in this application.